Why might ActiveController not work in Yii2?

Question

Yii

There is a model:

namespace app\models;
use yii\db\ActiveRecord;

class Book extends ActiveRecord
{
    public static function tableName()
    {
       return 'book';
    }
    public static function primaryKey()
    {
        return ['id'];
    }
    public function getAuthor()
    {
        return $this->hasOne(Author::className(), ['id' => 'author_id']);
    }
}

It is connected to the Author model, but everything is fine here, the links work fine in other functionality.
I need to organize the issuance of data in json format via RESTful by a separate controller.
First, I turned to the documentation .
And I copied and pasted the code of the controller itself, replacing it with my name of the model and controller, the simplest one given in the documentation:

namespace app\controllers;
use yii\rest\ActiveController;

class BookController extends ActiveController
{
    public $modelClass = 'app\models\Book';
}

Added to 'urlManager': 'rules' =>
According to the documentation, this is enough to get the finished API (finishing is still a secondary issue). But in fact, both through curl and through restlet_client (Chrome extension) I get:
status: 500 and PHP Fatal Error Class app\controllers\ActiveController; not found
I can't even guess what's wrong. This situation has me confused. I made a request to other controllers through restlet_client and received 200 and the entire page code. That is, it's not about the tools 100%, something is wrong with the code. What are the options? Why is the standard 100% working example from the documentation suddenly not working? And where could be the mistake?